Similarities do exist. The political system, the way they wage war (i do think that).
But i don't think that USA can be compared to The Roman Empire.
And neither of them are "evil empires"..
Still, i look on USA as an Empire. They are the only superpower in the world.
I said earlier that i think the way of waging war is quite similar,
but starting a war is a very different prosess.
Roman wars was just a result from ambitions, ambitions and yet ambitions.
The wars of the USA is a result from almost endless patriotism, and incrisingly larger paranoia.
(Acutally, i do think the Americans have good reason for it too..)
EDIT:
Oh, i'm sorry. If you think this has little to do with the Roman Empire i shouldn't post.
I'm not as good reading posts before i post myself as i should have been..